The present invention relates to methods for bonding substrates, such as polymer sheets to provide laminates for use in fabricating articles such as containers, and to novel laminates and adhesive compositions for laminating such materials.
The use of adhesives for bonding various similar and dissimilar materials is old and well known. However, difficulties still arise when dissimilar materials are to be bonded or laminated to one another, and these difficulties are frequently compounded when the laminates are to be subjected to various factors inimical to the adhesive characteristics of the materials.
One instance of such difficulties is illustrated by the laminated materials sought for use in the large-scale production of disposable containers, such as those used for coffee, soups, and other hot liquids. It is desirable to produce such containers easily and at a minimum of cost so they can be used by the consumer and discarded. It is further desirable that the containers be strong as well as attractively decorated and capable of receiving printing, lithography and the like.
It has accordingly been sought to provide a laminate of paper and polystyrene foam so that the paper can be decorated to provide an attractive appearance and the foam will provide impermeability to liquid contents and low heat transfer, in order that a cup of hot liquid can be comfortably held by the consumer. The dissimilarity of the porous hydrophilic paper substrate and the polystyrene has created problems in obtaining adequate adhesion, and this problem is especially severe wben the laminates are to be contacted with hot liquids. In fact, up to the present time, no satisfactory, readily produced laminates, such as those of paper and polystyrene foam have been available to withstand hot liquids.
U.S. Pat. No. 3,378,424 shows the application of polymeric coatings to fibrous substrates. The process there shows treatment of the fibrous substrate with an aqueous emulsion containing a wax and an ethylene-vinyl acetate copolymer. No solvent for the polymeric coating is involved.
U.S. Pat. No. 2,917,217 shows laminates of paper and polystyrene foam, and the adhesive recommended for use in a synthetic resin having a polyvinyl acetate base.
U.S. Pat. No. 2,510,908 shows an adhesive comprising polystyrene, toluene, and a triaryl phosphate plasticizer for bonding polystyrene to paper and other surfaces. The adhesive bonds are not exposed to aqueous or high-temperature environments. U.S. Pat. No. 3,112,235 shows an adhesive method utilizing borates and polyvinyl alcohol.
U.S. Pat. No. 2,628,180 shows an adhesive using styrene monomer, solvent, and an alkoxyethyl stearate evaporation retarder, while U.S. Pat. No. 2,975,093 relates to a process for laminating cellulosic sheets with one another by treating the surfaces of the sheets with polyvinyl alcohol solutions. Various other adhesive compositions and methods are shown in U.S. Pat. Nos. 3,135,648 and 2,434,106.